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NP Control with Optimal Sequence SVM 135
current is obviously very large (compare with last column of TABLE 23). A full set of graphs for
different load angles and modulation schemes is given in appendix 9.5.3.
m
θ
m
θ
(a)
(b)
Figure 95, (a) Maximum and (b) minimum NP currents in function of modulation depth and voltage
angle θ in pure reactive power operation
6.1.5.2 Average minimum and maximum NP currents
The average minimum and maximum NP currents over the fundamental period are a measure
for the NP control capacity. For low modulation depth, virtual vector sequences are available for
several phases. As a result, the NP current control capacity can be increased to 50% (of the peak
phase current) for all load angles at low modulation depths down to zero. For high modulation
depth, virtual vector sequences are available for one phase only and the effectiveness is depending
on the load angle. Nevertheless, there is a significant impact on the NP current control capacity in
both reactive and active power operation, as can be seen from Figure 96. Notably in the over
modulation region, the modified and virtual vector scheme still provides effective NP control
capacity. Note that for zero load angle, the unconstrained DC CM injection performs the same as
the real time NP current scheme; the green curve is not visible in the graph as it coincides with the
blue curve. Note that the red lines in Figure 96 (b) for minium and maximum average NP currents
over a fundamental period correspond with an averaging of the functions in Figure 95 over θ.
(a)
(b)
Figure 96, minimum and maximum average NP currents in function of load angle, modulation type
and modulation depth. Red: modified and virtual vector scheme, Blue: real time NP current scheme,
Green: unconstrained DC CM injection scheme. (a) ϕ = 0 (cos(ϕ) = 1), (b) ϕ = 1.56 (cos(ϕ) = 0.01)